The oxidation and reduction of various substrates in living organisms are of fundamental importance to life sustaining processes. Multi-electron transfer processes, although less frequent in nature are of equally great importance. Included among the latter are: the 6e- reduction of N2 to ammonia in nitrogenase, the 6ereduction of sulfite to sulfide and of nitrite to ammonia in sulfite and nitrite reductases respectively and the 4eoxidation of 2H2O to O2 in photosynthesis. This proposal is concerned with the synthesis and study of synthetic analogs for metalloenzymes involved in multielectron reductions. Specifically: the synthesis, structures, spectroscopic properties and reactivities of Fe/M/S (M=Mo, V) and Fe/S clusters will be the aims of this proposal. The recent discovery of an encapsulated light atom in the Fe/Mo/S center of nitrogenase has introduced a feature not previously encountered in the chemistry of M/S clusters in biology. The synthetic methodology needed to introduce light atoms (N, O, C?) in the interior of the Fe/M/S clusters is not known and must be developed. The role of such centers in enzymatic activity also is not known and must be determined. It is now clear that synthetic analogs for the Fe/M/S centers in the nitrogenases and presumably alternate nitrogenases must contain a central light atom as an integral structural unit. The reactivity of such synthetic analogs, once obtained, will be of great interest. New types of Fe/S clusters will be synthesized designed as models for the P-clusters of nitrogenase. Supramolecular assemblies with appended, redox active, Fe/S clusters will be synthesized, and their possible function in the multisite activation and catalytic reduction of dinitrogen and /or generation of dihydrogen from protons will be investigated.